In the fertilizer industry, there is a growing awareness of environmental concerns and the ability of a custom applicator to answer those concerns. As discussed in the co-pending related application identified above, a variable rate technology can be implemented using a plurality of maps containing soil-type information, current fertilizer levels and desired fertilizer levels, used in combination with a navigation system to create a chemical prescription.
As is well known, the three most common nutrient components of soil are nitrogen, phosphorous and potassium. Differing soil types, each of which may be categorized according to the relative proportions of sand, clay and silt, have differing percentages of these nutrients. Even like soil types can have differing percentages of these nutrients within agricultural land due to drainage characteristics, moisture content and erosion. Thus, fertilizer application systems need to account for the present levels of fertilizers at each location of the agricultural field to determine a chemical prescription when applying fertilizers to achieve desired fertilizer levels. One embodiment of the fertilizer application system discussed in the above-referenced copending application includes a plurality of maps storing soil types, and present and desired fertilizer levels within a field. Using a navigation system and a speed sensor, the system coordinates the vehicles location within the field to each of the maps to determine the application rate of fertilizers to attain the desired levels of fertilizers.
While navigation systems currently available are becoming increasingly more accurate in resolution, such as Global Positioning Systems, there still can be an alignment difficulty based on the inherent inaccuracies of the source data utilized to create the map. Thus, a closed-loop application system which would eliminate the coordination of the navigation positioning system to the soil and fertilizer maps, and would be an advancement over prior art systems. Up until now, soil analyzers capable of sampling soil for chemical content in near real-time were unavailable, thus requiring soil maps and fertilizer maps to be first created by a soil scientist, and then digitized for subsequent use by the application equipment. Due to various uncertainties in the analysis, these maps may differ from the real world conditions at time of fertilizer application due to time, weather, miscalculations, or a variety of other problems.
U.S. Pat. No. 5,044,756 to Gaultney et al. teaches a real-time soil organic matter sensor. This sensor is adapted to a vehicle to determine organic matter content of soil at a soil scene. This device uses a light source which generates light at a fixed frequency, and senses the intensity of the reflected light at the same fixed frequency to determine the organic matter content. This device is limited to obtaining only organic matter content of soil based upon a percentage of the reflected light of a fixed frequency, and does not form a portion of an fertilizer application system.